Mechanical connector utilizing interlocked threads to transfer torque

ABSTRACT

This invention builds up on technical features and on the industry experience with the use of Merlin™ family connectors. In addition to friction, structural means utilized to transfer high torsional loads include interlocked thread systems and may also include: dog-clutch teeth, shear pins, keys and splines, all used in isolation or in arbitrary combinations. Static and fatigue bending load capacities of the connectors remain high, while the axial load capacities may or may not be high, depending on the design requirements. Connectors according to this invention can be built as new, carefully optimized designs. In some cases upgrading existing Merlin™ family connector designs to increase they torque transfer capacities may be also feasible.

This application is a Divisional application of U.S. Utility patentapplication Ser. No. 15/782,835 for ENHANCEMENTS OF MECHANICAL CONNECTORTECHNOLOGY filed on Oct. 12, 2017 which is based on U.S. provisionalapplications No. 62/409,313 filed on Oct. 17, 2016 and incorporatedherein and it is a Continuation in Part (CIP) application following U.S.Utility patent application Ser. No. 15/239,696 for MECHANICAL CONNECTOROF LONG TORSIONAL AND BENDING FATIGUE LIFE filed on Aug. 17, 2016 andincorporated herein, which is based on U.S. provisional applications No.62/148,665 filed on Apr. 16, 2015 and No. 62/189,437 filed on Jul. 7,2015, and on PCT Application PCT/US16/28033 (WO/2016/168,707) filed Apr.18, 2016. U.S. provisional patent application 62/409,313 filed on Oct.17, 2016 introduces enhancements to mechanical connector technology.This application claims the benefits of priority related to U.S.provisional applications 62/148,665, 62/189,437 and 62/409,313 and toPCT application PCT/US16/28033 (WO/2016/168,707). It is noted that thereare also related applications: application Ser. No. 17/485,336 forTELESCOPICALLY ASSEMBLED MECHANICAL CONNECTOR filed on Sep. 25, 2021which is a CIP application following U.S. application Ser. No.16/920,350 for MECHANICAL CONNECTORS filed on Jul. 2, 2020 and issued asU.S. Pat. No. 11,156,313 on Oct. 26, 2021; this is a CIP Applicationfollowing U.S. Utility Patent Application already Ser. No. 15/782,825identified above. This application also follows British National EntryApplication GB176766.9 titled MECHANICAL CONNECTOR OF LONG TORSIONAL ANDBENDING FATIGUE LIFE lodged on Oct. 13, 2017 and granted as BritishPatent GB 2,556,691 on May 12, 2021 claiming for priority the same PCTApplication PCT/US16/28033 filed on Apr. 18, 2016 and its BritishDivisional Patent Application GB2100826.3 titled MECHANICAL CONNECTORUTILIZING INTERLOCKED THREADS TO TRANSFER TORQUE lodged on Jan. 21, 2021and granted as British Patent GB 2,591,878 on Nov. 16, 2021.

TECHNICAL FIELD

This invention relates to mechanical connectors used in any engineeringapplication, and in particular in offshore engineering at or near thesea surface, above or below the water surface, as well as anywhere inthe water column.

BACKGROUND ART

Mechanical connectors of the Merlin™ group (featured for example inGB1,573,945, GB2,033,518, GB2,099,529, GB2,113,335, U.S. Pat. Nos.5,964,486, 8,056,940, EP0,803,637, etc.) and types derived by thirdparties from the Merlin™ group of designs are widely used in OffshoreEngineering. Merlin™ is a registered name of the most widely usedconnector in the group that is manufactured by Oil States Industries.Similar connectors acting on the same principle are also manufactured byothers, but for simplicity all those designs are referred to herein asMerlin™ group, or Merlin™ family connectors. Those designs and theiradvantages are well known to anybody skilled in the art.

In particular, the Merlin™ group connectors known characterize with highstatic and fatigue strengths with regard to axial and bending loads, asrequired for traditional tendon, conductor, riser, etc. applications.The above traditional connectors do not typically experience high staticor fatigue torsional loads and their torsional load capacities arelimited to frictional resistance resulting from radial and axialconnector preload that could be augmented by the actual loading of theconnector. Accordingly the Merlin™ family connectors characterize withlimited torsional load capacities that may be difficult to controlaccurately by design means. In known connectors the box outside stressdiameters and the pin inside stress diameters are kept substantiallyconstant along the threaded segments of the said connectors. Minordepartures from that have been described in prior art literature, butthose are nowhere as pronounced as in novel connectors introducedherein. A background art mechanical connector is provided with a thread(zero pitch angle for background art connectors) on substantiallymatching frustoconical surfaces extending between two sets of metalnipple seals (annotation 140, see FIG. 2 ; note that metal seals 140 usethe same basic configuration and operation principle on background artconnectors, as they do on novel connectors). One of those sets of saidmetal nipple seals is located near an end of a box and the other saidset of said metal nipple seals is located near an end of a pin. It isknown to anybody skilled in the art that each of the above sets of thesaid metal nipple seals incorporates axially engaging, substantiallycylindrical surfaces with an outside surface and an inside surface of amale substantially cylindrical segment interacting radially through themechanism of a hoop stress with substantially matching surfaces of asubstantially cylindrical cavity.

Oil States Industries offers also a high torsional capacity Lynxconnector, but that connector is structurally different and it is notdesigned with particularly high torsional fatigue strength in mind. TheLynx is designed to resist accidental high loads.

Important design considerations pertaining to selecting heights ofprotrusions and depths of grooves used in the Merlin™ family connectorsat various axial locations of those connectors, preferable taper anglesat various locations as well as means to improve the telescopic stabbingin operations with the use of hydraulic pressure are disclosed forexample in U.S. Pat. No. 8,056,940. Those design features, or theirequivalents, can be optionally applied to these designs, whereverapplicable.

DISCLOSURE OF INVENTION

This invention builds up on technical features and on the industryexperience with the use of Merlin™ family connectors. Novel technicalstructural features, not used previously in the Merlin™ familyconnectors, are provided in order to handle high torsional loads. Inaddition to friction, structural means that are used in order totransfer high torsional loads include: dog-clutch teeth, fitted pins,keys, splines and interlocked thread systems, all used in isolation orin arbitrary combinations. Modifications in the shapes of the box andthe pin are introduced. Those are useful for weight control. The abovecan be used in particular in connectors designed for lower designpressures and for smaller piping/tubing diameters than are those usedtypically subsea. Additionally a use of assembly/disassembly fluids thatsolidify in at least some ranges of operational temperatures ofconnectors is introduced. Those include in particular resins or tar-likenon-metals and liquid metals solidifying in single phases as well as inmultiple phases like for example binary, ternary etc. eutectics.

Merlin family connectors and some of their third party derivatives canbe welded to the ends of pipes to be connected, or the pins and theboxes forming the connections can be shaped in the actual pipe used.Typically high yield strength and high quality materials are used forbuilding Merlin-family connectors, and the same or similarcharacteristics materials should be used for building connectorsaccording to this invention.

The following design enhancements of connectors are introduced herein:

-   -   modifications of shapes of boxes and/or pins for lower operating        pressures and assembly/disassembly pressures;    -   introduction of inside diameter (ID) fairings, outside diameter        (OD) fairings strengthening fins, planar, curved, box or        honeycomb stiffeners and web stiffeners for stiffness control,        buckling resistance, material saving and weight control;    -   modifications of thread tooth geometry that enhance leak        resistance & improve loading;    -   introduction of metallic and non-metallic assembly/disassembly        fluids that essentially solidify in the design ranges of        temperatures;    -   improvements in the solid to solid heat transfer between the pin        and the box and improvements in heat dissipation.

Static and fatigue bending load capacities of novel connectors remainhigh, while the axial load capacities may or may not be high, dependingon the design requirements. Depending on specific design requirementsand economic factors (like for example component cost and the size ofthe market expected) the engineer can select between two subgroups ofnovel connectors that feature:

-   -   Novel connectors adapting Merlin™ family connectors for        transferring high torque loads by adding high torque capacity        through optimized structural additions;    -   Novel connectors featuring structural elements that require        major design modifications.

The first subgroup includes:

-   -   Novel connectors utilizing fitted pins to transfer structurally        high torsional loads;    -   Novel connectors utilizing the dog-clutch principle to transfer        structurally high torsional loads;    -   Novel connectors utilizing the shaft-rotor type key systems to        transfer structurally high torsional loads.

The second subgroup includes:

-   -   Novel connectors utilizing the shaft-rotor spline connection        principle to transfer structurally high torsional loads.    -   Novel connectors utilizing the threaded connection principle to        transfer structurally high torsional loads.

Novel connectors belong to the said first subgroup may involve newdesigns or they may involve design modifications of known Merlin™ familyconnectors. The structural additions are introduced in the not veryhighly loaded regions of known connectors, or in regions where loadingpertaining to ‘traditional design loads’ on Merlin™ family connectorsare reduced. Retrofitting spare or retired known connectors with newstructural features and torque loading capabilities may be alsofeasible.

Novel connectors featuring the enhancements listed above can be built asnew, carefully optimized designs.

Novel connectors feature variable, including for example tapered designsof the outside (stress) diameters of connector boxes and variable,including for example tapered designs of the inside (stress) diametersof pins in order to extend the use of the Merlin™ family connectors foruse with smaller design pressures (and therefore reduced pressures usedfor the assembly and disassembly of connectors) in comparison with theMerlin™ family connectors that are typically used offshore. Tapering theOD makes the box shell more flexible and it also extends the use of theconnectors to sizes smaller than those typically used with Merlin™family connectors, i.e. 8⅝ inches (219.1 mm) and greater. Merlin™ familyconnectors used offshore are typically manufactured through the processof high precision, computer numerically controlled (CNC) single pointdiamond tool turning.

Other features facilitating the extending this connector technology andthe technology of the Merlin™ family connectors to smaller sizes involveincreasing the manufacturing accuracy (decreasing tolerances) byutilizing more accurate high precision manufacturing technology. Thatincludes for example using smaller, more accurate and/or more robustlybuilt lathes, grinding, polishing, electrochemical polishing,electrolytic polishing (electropolishing), tumbling, rumbling,barreling, vibratory finishing, burnishing, peening, laser peening,sandblasting, etc. that allow achieving a greater dimensional accuracythan does turning. 3-dimensional (3D) printing can also be used.

For applications where low weight of novel connectors (exampleaerospace) is of importance, it may be advisable to use smaller numbersof thread teeth and/or very ‘slim’ thread teeth profiles, even if thatmakes it impossible to make up connections without a use of apressurized fluid. The same can be utilized whenever the design lengthsavailable for tubing or piping are limited, which may require a use ofshort connector lengths and short overlapping segments between the boxand the pin.

This invention involves a mechanical connector provided with azero-pitch angle thread on substantially matching frustoconical surfacesof a box and a pin; whereas said mechanical connector provided with saidzero-pitch angle thread on said substantially matching frustoconicalsurfaces of said box and said pin characterizes with a provision of aplurality of structural arrangements designed to transfer torque betweensaid box and said pin of said mechanical connector provided with saidzero-pitch angle thread on said substantially matching frustoconicalsurfaces of said box and said pin, including a single said structuralarrangement designed to transfer torque between said box and said pin ofsaid mechanical connector provided with said zero-pitch angle thread onsaid substantially matching frustoconical surfaces of said box and saidpin; whereas said structural arrangements designed to transfer torquebetween said box and said pin of said mechanical connector provided withsaid zero-pitch angle thread on said substantially matchingfrustoconical surfaces of said box and said pin include at least one of:

-   -   a plurality of sets of splines, including a single set of        splines,    -   a plurality of dog-clutch teeth, including a single dog-clutch        tooth,    -   a plurality of fitted pins, including a single fitted pin,    -   a plurality of keys, including a single key,    -   a plurality of right-handed threads, including a single        right-handed thread, interlocking substantially with said        zero-pitch angle thread on said substantially matching        frustoconical surfaces of said box and said pin,    -   a plurality of left-handed threads, including a single        left-handed thread, interlocking substantially with said        zero-pitch angle thread on said substantially matching        frustoconical surfaces of said box and said pin,    -   a plurality of said right-handed threads, including said single        right-handed thread, interlocking substantially with said        plurality of said left-handed threads, including said single        left-handed thread;        whereas said structural arrangements designed to transfer torque        between said box and said pin of said mechanical connector        provided with said zero-pitch angle thread on said substantially        matching frustoconical surfaces of said box and said pin are        arranged individually or in combinations in said mechanical        connector provided with said zero-pitch angle thread on said        substantially matching frustoconical surfaces of said box and        said pin.

This invention involves a mechanical connector provided with a thread onsubstantially matching frustoconical surfaces of a box and a pin, saidsubstantially matching frustoconical surfaces of said box and said pinextending essentially between two sets of metal nipple seals, whereasone said set of said metal nipple seals is located near an end of saidbox and another said set of said metal nipple seals is located near anend of said pin and whereas each said set of said metal nipple sealsincorporates axially engaging, substantially cylindrical surfaces withan outside surface and an inside surface of a male substantiallycylindrical segment interacting radially through a mechanism of a hoopstress with substantially matching surfaces of a substantiallycylindrical cavity; whereas said sets of said metal nipple seals areused for sealing a cavity between said box and said pin that is filledwith an assembly/disassembly fluid; said mechanical connector providedwith said thread on said substantially matching frustoconical surfacesextending essentially between said two sets of said metal nipple sealscharacterizes with a provision of a structural arrangement designed totransfer torque between said box and said pin of said mechanicalconnector provided with said thread on said substantially matchingfrustoconical surfaces extending essentially between said two sets ofsaid metal nipple seals;

wherein said structural arrangement designed to transfer torque betweensaid box and said pin of said mechanical connector provided with saidthread on said substantially matching frustoconical surfaces of said boxand said pin includes at least one of:

-   -   a plurality of spline teeth,    -   a plurality of dog-clutch teeth, including a single dog-clutch        tooth,    -   a plurality of fitted pins, including a single fitted pin,    -   a plurality of keys,    -   a plurality of right-handed threads, including a single        right-handed thread, interlocking substantially with said thread        on said substantially matching frustoconical surfaces of said        box and said pin through the mechanism of at least one of:        -   an interlocking of said right-handed thread with said thread            on said substantially matching frustoconical surfaces of            said box and said pin having a zero-pitch angle,        -   an interlocking of said right-handed thread with said thread            on said substantially matching frustoconical surfaces of            said box and said pin having a left-handed thread,        -   an interlocking of said right-handed thread with said thread            on said substantially matching frustoconical surfaces of            said box and said pin having a right-handed thread with a            differing pitch,    -   a plurality of left-handed threads, including a single        left-handed thread, interlocking substantially with said thread        on said substantially matching frustoconical surfaces of said        box and said pin through the mechanism of at least one of:        -   an interlocking of said left-handed thread with said thread            on said substantially matching frustoconical surfaces of            said box and said pin having said zero-pitch angle,        -   an interlocking of said left-handed thread with said thread            on said substantially matching frustoconical surfaces of            said box and said pin having a right-handed thread,        -   an interlocking of said left-handed thread with said thread            on said substantially matching frustoconical surfaces of            said box and said pin having a left-handed thread with a            differing pitch;            whereas said structural arrangements designed to transfer            torque between said box and said pin are arranged            individually or in combinations in said mechanical connector            provided with said thread on said substantially matching            frustoconical surfaces of said box and said pin.

This invention involves a mechanical connector provided with a thread onsubstantially matching frustoconical surfaces of a box and a pin, saidsubstantially matching frustoconical surfaces of said box and said pinextending essentially between two sets of metal nipple seals, whereasone said set of said metal nipple seals is located near an end of saidbox and another said set of said metal nipple seals is located near anend of said pin and whereas each said set of said metal nipple sealsincorporates axially engaging, substantially cylindrical surfaces withan outside surface and an inside surface of a male substantiallycylindrical segment interacting radially through a mechanism of a hoopstress with substantially matching surfaces of a substantiallycylindrical cavity; whereas said sets of said metal nipple seals areused for sealing a cavity between said box and said pin that is filledwith an assembly/disassembly fluid; said mechanical connector providedwith said thread on said substantially matching frustoconical surfacesextending essentially between said two sets of said metal nipple sealsbeing characterized with design modifications introduced in order tocontrol weight, stiffness and buckling resistance incorporates at leastone of:

-   -   an outside (stress) diameter of said box of said mechanical        connector provided with said thread on said substantially        matching frustoconical surfaces of said box and said pin        incorporating a plurality of tapering surfaces or their        approximation, including a single tapering surface or its        approximation,    -   or an inside (stress) diameters of said pin of said mechanical        connector provided with said thread on said substantially        matching frustoconical surfaces of said box and said pin        incorporating a plurality of tapering surfaces or their        approximation, including a single tapering surface or its        approximation.

This invention involves a mechanical connector provided with a thread onsubstantially matching frustoconical surfaces of a box and a pin, saidsubstantially matching frustoconical surfaces of said box and said pinextending essentially between two sets of metal nipple seals, whereasone said set of said metal nipple seals is located near an end of saidbox and another said set of said metal nipple seals is located near anend of said pin and whereas each said set of said metal nipple sealsincorporates axially engaging, substantially cylindrical surfaces withan outside surface and an inside surface of a male substantiallycylindrical segment interacting radially through a mechanism of a hoopstress with substantially matching surfaces of a substantiallycylindrical cavity; whereas said sets of said metal nipple seals areused for sealing a cavity between said box and said pin that is filledwith an assembly/disassembly fluid;

wherein said mechanical connector provided with said thread on saidsubstantially matching frustoconical surfaces extending essentiallybetween said two sets of said metal nipple seals being characterizedwith design modifications introduced in order to control weight,stiffness and buckling resistance incorporates at least one of:

-   -   an outside (stress) diameter of said box of said mechanical        connector provided with said thread on said substantially        matching frustoconical surfaces of said box and said pin is        provided with a plurality of stiffener fins, including a single        stiffener fin;    -   or an inside (stress) diameters of said pin of said mechanical        connector provided with said thread on said substantially        matching frustoconical surfaces of said box and said pin is        provided with a plurality of stiffener fins, including a single        stiffener fin.

This invention involves a mechanical connector provided with a thread onsubstantially matching frustoconical surfaces of a box and a pin, saidsubstantially matching frustoconical surfaces of said box and said pinextending essentially between two sets of metal nipple seals, whereasone said set of said metal nipple seals is located near an end of saidbox and another said set of said metal nipple seals is located near anend of said pin and whereas each said set of said metal nipple sealsincorporates axially engaging, substantially cylindrical surfaces withan outside surface and an inside surface of a male substantiallycylindrical segment interacting radially through a mechanism of a hoopstress with substantially matching surfaces of a substantiallycylindrical cavity; whereas said sets of said metal nipple seals areused for sealing a cavity between said box and said pin that is filledwith an assembly/disassembly fluid;

wherein generatrices of interacting threads on said box and on said pinmismatch by design by at least 0.02°.

This invention involves a mechanical connector provided with a thread onsubstantially matching frustoconical surfaces of a box and a pin, saidsubstantially matching frustoconical surfaces of said box and said pinextending essentially between two sets of metal nipple seals, whereasone said set of said metal nipple seals is located near an end of saidbox and another said set of said metal nipple seals is located near anend of said pin and whereas each said set of said metal nipple sealsincorporates axially engaging, substantially cylindrical surfaces withan outside surface and an inside surface of a male substantiallycylindrical segment interacting radially through a mechanism of a hoopstress with substantially matching surfaces of a substantiallycylindrical cavity; whereas said sets of said metal nipple seals areused for sealing a cavity between said box and said pin that is filledwith an assembly/disassembly fluid;

whereas:

-   -   loaded sides of said thread on said substantially matching        frustoconical surfaces of said box and said pin are defined as        sides, an engagement of which prevents a disconnection of said        mechanical connector provided with said thread on said        substantially matching frustoconical surfaces of said box and        said pin,    -   unloaded sides of said thread on said substantially matching        frustoconical surfaces of said box and said pin are defined as        those sides of said thread on said substantially matching        frustoconical surfaces of said box and said pin that are not        said loaded sides of said thread on said substantially matching        frustoconical surfaces of said box and said pin,    -   each of thread generatrix angles Θ1 _(b), Θ2 _(b), Θ1 _(p), Θ2        _(p) is measured between a normal to an axis of said box or        between a normal to an axis of said pin and a thread generatrix        of said unloaded side of said thread on said substantially        matching frustoconical surfaces of said box and said pin or said        loaded side of said thread on said substantially matching        frustoconical surfaces of said box and said pin corresponding        respectively:        -   a box thread generatrix angle Θ1 _(b) is measured on said            unloaded side of said thread on said substantially matching            frustoconical surface of said box,        -   a box thread generatrix angle Θ2 _(b) is measured on said            loaded side of said thread on said substantially matching            frustoconical surface of said box,        -   a pin thread generatrix angle Θ1 _(p) is measured on said            unloaded side of said thread on said substantially matching            frustoconical surface of said pin,        -   a pin thread generatrix angle Θ2 _(p) is measured on said            loaded side of said thread on said substantially matching            frustoconical surface of said pin;            wherein said mechanical connector provided with said thread            on said substantially matching frustoconical surfaces of            said box and said pin is characterized by at least one of            absolute values of:    -   a thread generatrix mismatch angle |Θ1 _(b)−Θ1 _(p)|≥0.05°,    -   or a thread generatrix mismatch angle |Θ2 _(b)−Θ2 _(p)|≥0.05°.

This invention involves a mechanical connector provided with a thread onsubstantially matching frustoconical surfaces of a box and a pin, saidsubstantially matching frustoconical surfaces of said box and said pinextending essentially between two sets of metal nipple seals, whereasone said set of said metal nipple seals is located near an end of saidbox and another said set of said metal nipple seals is located near anend of said pin and whereas each said set of said metal nipple sealsincorporates axially engaging, substantially cylindrical surfaces withan outside surface and an inside surface of a male substantiallycylindrical segment interacting radially through a mechanism of a hoopstress with substantially matching surfaces of a substantiallycylindrical cavity; whereas said sets of said metal nipple seals areused for sealing a cavity between said box and said pin that is filledwith an assembly/disassembly fluid; said mechanical connector providedwith said thread on said substantially matching frustoconical surfacesextending essentially between said two sets of said metal nipple sealswhereas:

-   -   loaded sides of said thread on said substantially matching        frustoconical surfaces of said box and said pin are defined as        sides, an engagement of which prevents a disconnection of said        mechanical connector,    -   unloaded sides of said thread on said substantially matching        frustoconical surfaces of said box and said pin are defined as        those sides of said thread on said substantially matching        frustoconical surfaces of said box and said pin that are not        said loaded sides of said thread on said substantially matching        frustoconical surfaces of said box and said pin,    -   each of thread generatrix angles Θ1 _(b), Θ2 _(b), Θ1 _(p), Θ2        _(p) is measured between a normal to an axis of said box or        between a normal to an axis of said pin and a thread generatrix        of said unloaded side of said thread on said substantially        matching frustoconical surfaces of said box and said pin or said        loaded side of said thread on said substantially matching        frustoconical surfaces of said box and said pin corresponding        respectively:        -   a box thread generatrix angle Θ1 _(b) is measured on said            unloaded side of said thread on said substantially matching            frustoconical surface of said box,        -   a box thread generatrix angle Θ2 _(b) is measured on said            loaded side of said thread on said substantially matching            frustoconical surface of said box,        -   a pin thread generatrix angle Θ1 _(p) is measured on said            unloaded side of said thread on said substantially matching            frustoconical surface of said pin,        -   a pin thread generatrix angle Θ2 _(p) is measured on said            loaded side of said thread on said substantially matching            frustoconical surface of said pin;    -   wherein said mechanical connector provided with said thread on        said substantially matching frustoconical surfaces of said box        and said pin is characterized by at least one of absolute values        of:        -   a thread generatrix mismatch angle |Θ1 _(b)−Θ1 _(p)|≥0.02°,        -   or a thread generatrix mismatch angle |Θ2 _(b)−Θ2            _(p)|≥0.02°.

This invention involves also the use of pressurized fluids that solidifyin operational conditions (including liquid metals and metallic alloys)and those fluids are typically liquid in order to assemble ordisassemble Merlin™ family connectors and/or mechanical connectors oflong torsional and bending fatigue life.

This invention involves a mechanical connector provided with a thread onsubstantially matching frustoconical surfaces of a box and a pin, saidsubstantially matching frustoconical surfaces of said box and said pinextending essentially between two sets of metal nipple seals, whereasone said set of said metal nipple seals is located near an end of a boxand another said set of said metal nipple seals is located near an endof a pin and whereas each said set of said metal nipple sealsincorporates axially engaging, substantially cylindrical surfaces withan outside surface and an inside surface of a male substantiallycylindrical segment interacting radially through a mechanism of a hoopstress with substantially matching surfaces of a substantiallycylindrical cavity; whereas said sets of said metal nipple seals areused for sealing a cavity between said box and said pin that is filledwith an assembly/disassembly fluid;

and whereas said mechanical connector provided with said thread on saidsubstantially matching frustoconical surfaces extending essentiallybetween said two sets of said metal nipple seals includes saidassembly/disassembly fluid remaining liquid during assembly/disassemblyoperations;wherein after an assembly operation said assembly/disassembly fluid isallowed to solidify in an assembled condition of said mechanicalconnector and remains essentially solid, thus becoming essentially asolid seal.

This invention involves a mechanical connector provided with a thread onsubstantially matching frustoconical surfaces of a box and a pin, saidsubstantially matching frustoconical surfaces of said box and said pinextending essentially between two sets of nipple seals, whereas one saidset of said nipple seals is located near an end of a box and anothersaid set of said nipple seals is located near an end of a pin andwhereas each said set of said nipple seals incorporates axiallyengaging, substantially cylindrical surfaces with an outside surface andan inside surface of a male substantially cylindrical segmentinteracting radially through a mechanism of a hoop stress withsubstantially matching surfaces of a substantially cylindrical cavity;whereas said sets of said nipple seals are used for sealing a cavitybetween said box and said pin that is filled with anassembly/disassembly fluid;

and whereas said mechanical connector provided with said thread on saidsubstantially matching frustoconical surfaces extending essentiallybetween said two sets of said nipple seals includes saidassembly/disassembly fluid remaining liquid during assembly/disassemblyoperations;wherein after an assembly operation said assembly/disassembly fluid isallowed to solidify in an assembled condition of said mechanicalconnector and remain essentially solid thus becoming essentially a solidseal.

Depending on specific design requirements and economic factors (like forexample component cost and the size of the market expected) the engineercan select between two subgroups of novel connectors that feature:

-   -   Novel connectors adapting Merlin™ family connectors for        transferring high torque loads by adding high torque capacity        through optimized structural additions; Novel connectors        featuring structural elements that require major design        modifications.

The first subgroup includes:

-   -   Novel connectors utilizing fitted pins to transfer structurally        high torsional loads;    -   Novel connectors utilizing the dog-clutch principle to transfer        structurally high torsional loads;    -   Novel connectors utilizing the shaft-rotor type key systems to        transfer structurally high torsional loads.

The second subgroup includes:

-   -   Novel connectors utilizing the shaft-rotor spline connection        principle to transfer structurally high torsional loads.    -   Novel connectors utilizing the threaded connection principle to        transfer structurally high torsional loads.

Novel connectors belonging to the said first subgroup may include newdesigns or they may involve design modifications of known Merlin™ familyconnectors. The structural additions are introduced in the not veryhighly loaded regions of known connectors, or in regions where loadingpertaining to ‘traditional design loads’ on Merlin™ family connectorsare reduced. Retrofitting spare or retired known connectors with newstructural features and torque loading capabilities may be alsofeasible.

Novel connectors belonging to the said second subgroup require newdesign.

This invention involves a mechanical connector, whereas a connectionbetween a pin and a box of said mechanical connector is effected by theprinciple of zero-pitch angle threads provided on an essentially outsidesurface of said pin interacting axially and radially by means of axialand radial pretensions with essentially matching zero-pitch anglethreads provided on an essentially inside surface of said box; whereassaid zero-pitch angle threads provided on said essentially outsidesurface of said pin and said essentially matching zero-pitch anglethreads provided on said essentially inside surface of said box arearranged along a frustoconical pitch diameter surface that isessentially common to said essentially outside surface of said pin andto said essentially inside surface of said box; said mechanicalconnector being provided with structural means for transferring torquebetween said pin and said box, whereas said mechanical connector hasstatic and fatigue torsional and bending load capacities controlled bydesign means and said mechanical connector is also capable oftransferring axial loads between said pin and said box of saidmechanical connector;

said structural means for transferring torque between said pin and saidbox including:

-   -   a plurality of sets of splines provided on a plurality of        essentially matching surface sets of interactions between said        pin and said box, including a single essentially matching        surface set of interaction between said pin and said box; and        also including    -   a plurality of dog-clutch type teeth provided on a plurality of        essentially matching surface sets of interactions between said        pin and said box, including a single essentially matching        surface set of interaction between said pin and said box; and        also including    -   a plurality of fitted pins, including a single fitted pin,        whereas said plurality of said fitted pins is arranged along a        plurality of essentially matching surface sets between said pin        and set box, including a single essentially matching interaction        surface set between said pin and said box, whereas the transfer        of said torque is effected by interactions of said pin with said        plurality of said fitted pins and at the same time by an        interaction of said plurality of said fitted pins with said box;        and also including    -   a plurality of keys, including a single key, whereas said        plurality of said keys is arranged along a plurality of        essentially matching surface sets between said pin and set box,        including a single essentially matching surface set between said        pin and said box, whereas the transfer of said torque is        effected by interactions of said pin with said plurality of said        keys and at the same time by an interaction of said plurality of        said keys with said box; and also including    -   right-handed threads provided on a plurality of essentially        matching surface sets of interactions between said pin and said        box, including a single essentially matching surface set of        interaction between said pin and said box; and also including        left-handed threads provided on a plurality of essentially        matching surface sets of interactions between said pin and said        box, including a single essentially matching surface set of        interaction between said pin and said box; and also including    -   right-handed threads and left-handed threads provided on a        plurality of essentially matching surface sets of interactions        between said pin and said box, including a single essentially        matching surface set of interaction between said pin and said        box.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 through 20 are provided to facilitate understanding of keyfeatures and key implementations of novel connectors.

FIG. 1 shows an exploded view of a novel connector utilizing splinetorque transfer.

FIG. 2 shows a cross-section through one side of a novel connectorutilizing spline torque transfer (shown in FIG. 1 ).

FIG. 3 presents a half view of a novel connector featuring a key torquetransfer arrangement.

FIG. 4 shows a detail of a key interacting with a box of a novelconnector.

FIG. 5 presents a half view of a novel connector featuring fitted pintorque transfer arrangement.

FIG. 6 shows details of fitted pins interacting with pins and boxes ofnovel connectors, one for each end of the interacting surfaces.

FIG. 7 depicts a detail of a novel connector assembled, whereas thedog-clutch torque transfer principle is utilized near the outsidesurfaces of the pin and the box. The dog-clutch teeth utilize the fullmaterial thickness available between the metal seal region and theoutside surface of the connector.

FIG. 8 depicts a detail of a novel connector in an exploded view,whereas the dog-clutch torque transfer principle is utilized near theoutside surfaces of the pin and the box. The dog-clutch teeth utilize apart of the material thickness available between the metal seal regionand the outside surface of the connector.

FIG. 9 depicts a detail of a novel connector assembled, whereas thedog-clutch torque transfer principle is utilized near the insidesurfaces of the pin and the box. The dog-clutch teeth utilize the fullmaterial thickness available between the metal seal region and theinside surface of the connector.

FIG. 10 depicts a detail of a novel connector in an exploded view,whereas the dog-clutch torque transfer principle is utilized near theinside surfaces of the pin and the box. The dog-clutch teeth utilize apart of the material thickness available between the metal seal regionand the inside surface of the connector.

FIGS. 11 a through 11 x depict examples of schematic representations ofmany design implementations of novel connectors that utilize forstructural torque transfer:

the spline connection principle;

the key connection principle;

the fitted (shear) pin connection principle;

the dog-clutch connection principle;

the interlocking threads connection principle.

FIGS. 11 a through 11 x depict for the sake of example designimplementations of the above listed torque transfer mechanisms usedseparately and in combinations. Variations in structural segmentsequencing along the example connectors shown are also featured.

FIG. 12 depicts schematically a segment of a novel connector thatcombines the dog-clutch and the fitted (shear) pin principles. The hightorque capacity region is located near the external metal seals and thetorque bearing protrusions extend partly through the wall thickness ofthe box.

FIG. 13 depicts schematically a segment of a novel connector thatcombines the dog-clutch and the fitted (shear) pin principles. The hightorque capacity region is located near the internal metal seals and thetorque bearing protrusions extend partly through the wall thickness ofthe pin.

FIGS. 14 a through 14 e depict an example detail half view of arelatively low pressure (LP) to medium pressure (MP) connector providedwith novel structural modifications. Several examples of pin designdetails are featured.

FIGS. 15 a through 15 c depict example detail half views of LP to MPconnector box designs provided with novel structural modifications.

FIG. 16 depicts an example detail half view of a novel relatively highpressure (HP) connector design featuring axisymmetric threads.

FIG. 17 depicts an example detail half view of a novel HP connectordesign featuring axisymmetric threads and shear fitted pins arrangednear the outside metal (nipple) seals.

FIGS. 18 a through 18 c depict example design details of novelmechanical connectors.

FIG. 19 depicts schematically optional thread crest geometrymodifications.

FIG. 20 depicts a detail of a novel connector box interacting with a pinfeaturing a novel use of an assembly/disassembly fluid solidified incavities.

MODES OF CARRYING OUT THE INVENTION

The high structural torsional capacities of novel connectors areachieved by incorporating high capacity torque transfer components inthe design of the connectors, while the high torsional fatigue life isachieved by optimally shaping and accurately finishing the surfaces ofcomponents that transfer high torques between the objects connected. Theobjects connected can involve pipe or tube segments and/or elements ofoffshore or onshore structures. The said novel connectors incorporatealso structural elements typical to the design of the Merlin™ familyconnectors that provide them with high bending capacities, and whereverrequired also with high axial load capacities.

Several implementations of novel connectors are depicted on FIGS. 1through 20 .

FIGS. 1 and 2 show a novel connector featuring spline torque transferarrangement 160. FIG. 1 shows an exploded view of box 100 and pin 110,while FIG. 2 shows a cross-section through the same connector assembled.

It is noted that spline system (set) 160, 165 as shown in FIGS. 1 and 2can be also incorporated in FIG. 3 , FIG. 5 , it can be combined withany of FIGS. 7 through 10 or with FIGS. 11 a through 11 c, 11 e, 11 f,11 k, 11 s, 11 t, 11 w , 12, 13, 14 a, 15 a through 17, 18 c and/or 20similarly to the arrangement depicted for a sake of examples on FIGS. 11d, 11 g through 11 j, 11 i through 11 p, 11 r, 11 u, 11 v and/or 11 x.All the above highlighted combinations of structural torque transferprinciples represent feasible designs of novel connectors.

In addition to spline torque transfer arrangement 160 this connectorimplements typical Merlin™ family features that are well known to thoseskilled in the art. The assembly and disassembly of all novel connectorsfeatured herein are similar and they are briefly outlined here byreference to FIGS. 1 and 2 .

Most novel connectors featured can be assembled either simply bytelescopic stabbing in, or they may need to be assembled with the aid offluid pressure contracting the pin and expanding the box, which is aprinciple well known to those skilled in the art. That is carried outsimilarly to the corresponding operational procedures relevant to theMerlin™-family connectors and some of their derivatives. Theassembly/disassembly of novel connectors is reversible, i.e. they can bedisassembled using fluid pressure and reassembled again. The assemblyand the disassembly can be carried out above or below the water surface.

Important design considerations pertaining to selecting heights ofprotrusions and depths of grooves used in the Merlin™ family connectorsat various axial locations of those connectors, as well, preferabletaper angles at various locations as well as means to improve thetelescopic operations with the use of hydraulic pressure are disclosedfor example in U.S. Pat. No. 8,056,940 and those in general apply toimplementations of this invention described herein. Those designfeatures, or their equivalents, can be optionally applied to thesedesigns, where applicable.

Metal to metal (nipple) seals 140 are used to seal a cavity between box100 and pin 110 that is filled with an assembly/disassembly fluid at thestage when the connector is only initially assembled. Metal to metalseals 140 seal the said cavity, while the fluid is delivered throughport 170. Nipple seals 140 incorporate axially engaging, substantiallycylindrical surfaces, whereas the outside and the inside surfaces ofmale cylindrical segments interact radially through the mechanism ofhoop stress and interference fit with substantially matching surfaces offemale cylindrical cavities. Fluid pressure expands box 100 and‘contracts’ pin 110 in the radial direction through the mechanisms ofhoop straining and meridional bending. The relation between the hoopstress(ing) σ and the hoop strain(ing) ϵ is known to anybody skilled inthe art, because it is expressed by the Hooke's Law: σ=ϵ·E, where E isthe Young modulus. That enables the final assembly stroke in the axialdirection that makes up the connection by engaging zero-pitch anglethreads 150, 155 of box 100 and pin 110. Axisymmetric, zero-pitch anglegrooves (threads) 150, 155 can engage only in the correct axial positiondue to the use of non-uniform axial pitch of thread 155. Axisymmetric,zero-pitch angle threads 150, 155 are responsible for the transfer ofaxial and bending loads as well as for the axial and radialpre-stressing of the connector. Excess assembly/disassembly fluid isremoved through fluid outlet ports 130 near each end of the connector.

High torsional and bending load capacity novel connectors optionally,but quite often require precisely accurate azimuth angle orientations ofbox 100 relative pin 110. The azimuth orientation angles of box 100relative pin 110 are modified by rotating pin 110 relative box 100around the axis of the connector. In a case the azimuth assembly angleis specified, spline set (system) 160, 165 can engage only in thecorrect circumferential position due to the use of non-uniform pitch oftrough 165 (and of the matching spline tooth, not visible) in thecircumferential direction, so that the novel connector can be assembledin only the prescribed design azimuth orientation. That is most oftenthe case.

In the connector shown in FIGS. 1 and 2 spline system (set) 160, 165 isarranged on cylindrical segments of box 100 and pin 110, which isoptional and preferable, but splines can also be shaped along taperedsurfaces, essentially matching the average local taper angles of thecontact surfaces of box 100 and pin 110.

Similarly to splines used in machine engineering, splines 160 and 165can be parallel-sided, they can have involute shaped sides, they canhave triangularly shaped spline teeth, they can have straight teethinteracting with involute shaped teeth, etc., as required. If necessaryradial and circumferential pre-loads can be used by utilizing a requireddegree of interference fitting between spline teeth 160, 165 of box 100and pin 110. The latter is often the case depending on the designrequirements, as it typically is in Merlin™ family connectors withregard to the axial and radial pre-loading. Spline teeth 160, 165 of theconnector shown in FIGS. 1 and 2 are parallel-sided as an example only.

Design features typically used for assembling/disassembling theconnectors shown in FIGS. 1 through 20 are deliberately omitted from thedrawings for simplicity.

FIG. 3 presents a half view of a novel connector featuring key 305torque transfer arrangement. For simplicity only box 300 and pin 310 areannotated, the remaining design features shown are analogous to thosealready explained.

FIG. 4 shows a detail of key 305 interacting with box 300 of theconnector in FIG. 3 . Key 305 shown in FIGS. 3 and 4 is sunk in pin 310.Gap 307 is shown between outside face 302 of key 305 and the depth ofthe key groove provided in box 300. Axisymmetric, zero-pitch anglethread is designated with 350 and 355; 355 is pertaining to non-uniformaxial pitch grooving. The longitudinal axis of key 305 shown is parallelto the average taper of the interacting surfaces of box 300 and pin 310along the length of the key, which is preferred, but that does not needbe the case in other designs.

The shape of outside face 302 of key 305 is impossible to see in thefigures, but for the sake of an example it is shown flat. In order toallow for some bending rigidity of key 305 during the final stage of theassembly, while box 300 and pin 310 flex in meridional bending becauseof a pressurization, groove 315 can be optionally provided. Groove 315may not be required in cases when outside face 302 of key 305 is roundedto match the outside major diameters of the axisymmetric grooving of pin310 (not shown in FIG. 4 and not annotated on FIG. 3 ). Rounding outsideface 302 of key 305 is preferable, either to match the outside contourof major diameters of the axisymmetric pin grooving, or equal to theminimum value of the major diameter of the axisymmetric pin groovingalong the length of key 305, so that the outside corners of key 305(sides of outside face 302) never protrude outside of the contour of theadjacent grooving of pin 310. Key 305 is best interference fitted intoits channel in pin 310, and preferably also (preferably loosely) boltedto pin 310 (optional screw not shown) or otherwise secured, in order toavoid a possibility of jamming during a disassembly or assembly of theconnector. The sides of key 305 are preferably also interference fittedinto the key channel in box 300.

In FIGS. 3 and 4 key 305 shown is double-rounded, but that is for thesake of an example only. Practically all types of key connections usedin machine engineering can be used with novel connectors. Those includefeather keys, square keys, flat keys, beveled keys, Woodruff keys, taperkeys, etc.

The key inserts can be alternatively provided with circular, oval,elliptical, or other curvilinear cross-sections. It is noted, however,that more machine-connection-like key cross section shapes, like squareor rectangular cross sections with only slightly rounded edges havehigher bearing load capacities than have those provided by keys havingcircular or elliptical cross sections.

Depending on the torque capacity of the connector required for aparticular design, multiple keys can be arranged around thecircumference of the connector (multiple o'clock positions), which ispreferably the case. Those keys can be arranged in one circumferentialrow, like in case of FIG. 3, 11 f, 11 l, 11 r, 11 w or/and 11 x, withadditional keys not visible, or in several rows (see schematicillustrations in FIG. 11 e ), in staggered rows or in irregulararrangements (see schematic illustration in FIG. 11 f ). It is notedthat key system 305 as shown on FIG. 4 can be also incorporated in thedesign shown on FIG. 5 , it can be combined with any of FIGS. 7 through10 or with any of FIGS. 11 a through 11 d, 11 g through 11 k, 11 sthrough 11 q, 11 s through 11 v, 12, 13, 14 a through 14 e, 15 a through15 c and/or 16 through 20. All the above highlighted combinationsrepresent feasible designs of novel connectors.

In a case of an ‘off a shelf’, or retrofitted Merlin™ family connectorbeing adapted to carry high torsional loads, it may be acceptable tosacrifice some of the original axial and even bending capacity of theconnector in order to upgrade its torsional load capacity by addingsystems (sets) of keys 305.

If required, keys 305 are typically arranged around the circumference ina non-uniform circumferential pitch or/and pattern, in order to assurethe connector assembly with the prescribed azimuth orientation of box300 relative pin 310.

FIG. 5 presents a half view of a novel connector featuring fitted pin505 torque transfer arrangements. Multiple fitted pins sets 505 can bearranged around the circumference of the connector in the region of oneof the connector ends or simultaneously in regions of both ends as it isshown on FIG. 5 . The use of fitted pins 505 simultaneously at bothconnector ends is preferable, because that limits frictional loaddifferential between the interaction surfaces of box 500 and pin 510.Fitted pins 505 can be arranged in a single row at each end, or inmultiple rows (sets) that may or may not be staggered with regard toeach other in the radial and/or circumferential direction(s), see forexample FIG. 17 . Only one row of fitted pins 505 is shown near each endin FIG. 5 , for the sake of an example. If required, fitted pins 505 aretypically arranged with a non-uniform circumferential pitch or patternin order to assure the connector assembly with the correct azimuthorientation of box 500 relative pin 510.

FIG. 6 shows details of fitted pins 505, 605 interacting with pins 510,610 and with boxes 500, 600 according to this invention, one for eachend of the interacting surfaces. The top detail depicted in FIG. 6 isthat of the connector shown in FIG. 5 ; see the bottom right corner ofFIG. 5 . The bottom detail in FIG. 6 is that of another similarconnector, note the differing dimensional proportions of box 600, pin610 and fitted pin 605. In particular note circumferential groove 615 inthe box that is used in order to increase locally the meridionalflexibility of box 600.

Similar grooves or systems of multiple grooves increasing locally thestructural flexibility can be arranged in corresponding locations or inother regions of boxes and/or pins, in particular in the regionsadjacent to metal seals. Depending on particular design requirementsthose may be beneficial in any connector depicted on FIGS. 1 through 20or otherwise discussed herein.

Connectors featuring fitted pins 505, 605 can be economical in design,retrofitted with fitted pins or otherwise adapted for particular designrequirements, because fitted pins 505, 605 or alike can be easilylocated in regions of relatively low structural loading. Holes to fitfitted pins 505, 605 are relatively easy to drill and shim to whatevergeometries may be required. Typically interference fitting of fittedpins 505, 605 or alike may be required depending on particular designneeds.

Fitted pins 505, 605 can be optionally screwed into one of the partsbeing connected or/and bonded with an adhesive, see also FIGS. 12, 13,17 and 18 b. O-rings, metal ring seals or other sealing arrangements canbe used in order to protect fitted pins 505, 605 from seawater and frominternal fluids, as applicable. Corrosion Resistant Alloys (CRAs),titanium alloys, aluminum alloys, magnesium alloys, nickel based alloys,steels, other materials, cladding with CRAs, weld overlaying with CRAsor encapsulating of interacting regions in protective resins, etc. canbe used with novel connectors featured herein. It is noted that fittedpins 505, 605 as shown on FIG. 6 can be also incorporated in the designsshown on FIGS. 1 through 3 , or they can be combined with any of FIGS. 7through 10 or with any of FIGS. 11 a through 11 l, 11 n , and 11 sthrough 11 v and/or FIG. 11 x . All the above highlighted combinationsrepresent feasible designs of novel connectors.

FIG. 7 depicts a detail of a novel connector assembled. The dog-clutchtorque transfer principle is utilized near the outside surfaces of pin710 and box 700. Dog-clutch teeth 780, 706, 716 utilize the fullmaterial thickness available between the metal seal region and theoutside surface of the connector, which is not fully visible on thefigure.

If required, dog-clutch teeth 780, 706, 716 are typically arrangedaround the circumference in a non-uniform circumferential pitch or/andpattern, in order to assure the connector assembly with the correctazimuth orientation of box 700 relative pin 710. Teeth 706/716 have forthat purpose different circumferential pitch than teeth 780 have.

FIG. 8 depicts in an exploded view a detail of a novel connector. Thedog-clutch torque transfer principle is utilized near the outsidesurfaces of pin 810 and box 800. Dog-clutch teeth 880, 806, 816 utilizea partial material thickness available between the metal seal region andthe outside surface of the connector.

It is known to anybody skilled in the art that long life torsionalfatigue strength of circular cross-section components (like for exampleturbine shafts) is less sensitive to the working cross-section changesthan bending fatigue is. However, for this application high torsionalfatigue strength is important and the preferred designs utilizerelatively large fillet radii 702, 802 and 712, 812 for the concaveregions of component edges. In particular large fillet radii 702, 802are used on FIGS. 7 and 8 for box 700, 800 concave edge regions andlarge fillet radii 712, 812 are used for pin 710, 810 concave edgeregions. For convex edge regions the shapes are not critical for fatiguelife and chamfers 704, 804 are shown for the convex edge regions ofboxes and 714, 814 for the convex edge regions of pins, but fillets canbe also used instead. High torsional load capacity arrangements 780,880, 706, 806, 716, 816 shown feature non-uniform circumferential pitchof shapes 706, 806 and 716, 816 on boxes 700, 800 and pins 710, 810respectively, in order to assure that the connector can only beassembled in its prescribed azimuth orientation of pins 710, 810relative boxes 700, 800, respectively.

FIG. 9 depicts a detail of a novel connector assembled. The dog-clutchtorque transfer principle is utilized near the inside surfaces of pin910 and box 900. Dog-clutch teeth 990, 996 utilize the full materialthickness available between the metal seal region and the inside surfaceof the connector, which is not fully visible on the figure.

If required, dog-clutch teeth 990, 996 are typically arranged around thecircumference in a non-uniform circumferential pitch or/and pattern, inorder to assure the connector assembly with the prescribed azimuthorientation of box 900 relative pin 910. Teeth 996 have for that purposedifferent circumferential pitch than teeth 990 have.

FIG. 10 depicts in an exploded view a detail of a novel connector. Thedog-clutch torque transfer principle is utilized near the insidesurfaces of pin 1010 and box 1000. Dog-clutch teeth 1080, 1006, 1016utilize a partial material thickness available between the metal sealregion and the inside surface of the connector.

If required, dog-clutch teeth 1080, 1006, 1016 are typically arrangedaround the circumference in a non-uniform circumferential pitch or/andpattern, in order to assure the connector assembly with the prescribedazimuth orientation of box 1000 relative pin 1010. Teeth 1006/1016 havefor that purpose different circumferential pitch than teeth 1080 have.

For applications where high torsional fatigue strength is important andthe preferred designs utilize relatively large fillet radii 1002 and1012 for concave regions of component edges. In particular large filletradii 1002 are used for box 1000 concave edge regions and large filletradii 1012 are used for pin 1010 concave edge regions. For convex edgeregions the shapes are not critical for torsional strength and chamfers1004 are shown for the convex edge regions of box 1000 and 1014 for theconvex regions of edges of pin 1010, but fillets can be also usedinstead.

The design of the protruding teeth and matching hollows carryingtorsional loads can be reversed between the boxes and the pins withoutaffecting the functionality of this invention in the examples shown onFIGS. 7 through 10 . A mixed reversed/not reversed design can also beused instead of that shown.

Connectors featuring the dog-clutch torque transfer arrangements can beeconomical in design for particular requirements, because torquetransfer teeth 780, 706, 716, 880, 806, 816, 990, 996, 1006, 1016 can beeasily located in regions of relatively low structural loading as shownin FIGS. 7 through 10, 12 and/or 13 . Dog-clutch teeth arrangements likethose shown in details on FIGS. 7 through 10 can be also incorporatedfor example in any of the designs shown on FIGS. 11 a through 11 m, 11o, 11 q, 11 s, 11 u, 11 v, and/or 14 a through 20. All the abovehighlighted combinations represent feasible designs of novel connectors.

Whenever the torque transfer arrangements are located simultaneously onboth ends (near both metal seal systems) in the same connector, novelconnectors utilizing fitted pins 505, 605 or dog-clutch torquetransferring teeth 780, 706, 716, 880, 806, 816, 990, 996, 1006, 1016characterize with most of the torque being transferred through theconnector structures, while largely by-passing those main contactsurfaces between the boxes and the pins that transfer the axial andbending loads.

FIGS. 11 a through 11 x depict for the sake of example designimplementations of torque transfer mechanisms featured used separatelyand in combinations. Variations in structural segment sequencing alongthe example connectors shown are also featured.

Example design implementations of novel mechanical connectors shown inFIGS. 11 a through 11 x provide differing load transfer functionsbetween box 1100 and pin 1110 are separated longitudinally into segments(sets). Surfaces 1111 of frustoconical pitch diameters (averageddiameter) are depicted schematically with dashed lines. Those extendbetween metal seals near each of the connectors, which are shown onFIGS. 11 a through 11 x with short lines parallel to the connector axes,but not annotated. Groove/protrusions systems (also referred to hereinas grooving) along frustoconical surfaces 1111 are shown schematicallywith groups of thin continuous lines. In general, the taper angles ofthe frustoconical surfaces of box 1100 and pin 1110 vary along thelengths of the connectors. The same is in general the case with otherconnectors like those shown on FIGS. 1 through 20 . Fitted (shear) pinsystems (sets) are indicated with rows of hollow shapes with barbs.Dog-clutch tooth systems are shown with rectangular zig-zag lines.

Because generic families of connectors are represented onlyschematically on FIGS. 11 a through 11 x , the same generic annotationsare used for simplicity on FIGS. 11 a through 11 x for all the genericcomponents corresponding in connectors of differing designs:

-   -   Known types of grooving (thread) providing static and fatigue        transfer of axial and bending loads are annotated 1140        (axisymmetric, zero pitch angle);    -   Thread grooving featuring absolute values of pitch angles (fixed        or variable) greater than 0° and smaller than 90° according to        this invention are annotated 1120 and 1121 for general        left-handed and general right-handed threads respectively;        additionally left handed threads and right handed threads that        have pitches differing (i.e. greater or smaller) from those        annotated 1120 and/or 1121 used in the same connector are        annotated 1125 and 1126, respectively. Groovings 1120, 1121,        1125 and 1126 combine the functions of transfer of axial,        bending and torsional static and dynamic (fatigue) loads;    -   Spline (grooving) sets according to this invention that        transfers torsional static and dynamic loads are annotated 1130        (absolute value pitch angles equal to or close to 90°);    -   Systems (sets) of keys used for torque transfer are annotated        1107 for keys arranged in circumferential rows and 1117 for        axially staggered key patterns, or for keys distributed        irregularly on surfaces 1111;    -   Systems (sets) of fitted shear pins used for torque transfer are        annotated 1150;    -   Systems (sets) of dog-clutch teeth used to transfer torque and        situated in the outside or in the inside abutment areas are        annotated 1160.

The numbers and/or sequences of segment (set) types shown in anyschematic view included on FIGS. 11 a through 11 x and their relativeaxial arrangements are incidental and these values/features can bemodified arbitrarily without changing the type of implementation of thisinvention.

FIG. 11 a depicts an example implementation of a novel connectorfeaturing two segments with grooving (thread) type 1140 and one segmentwith left-handed grooving (thread) type 1120. The example shown in FIG.11 a equally represents its mirror image with a replacement of grooving(thread) type 1120 with right-handed grooving (thread) type 1121, asshown on FIG. 11 k.

FIG. 11 b depicts an example novel connector featuring two segments withgrooving type 1140 and two non-zero pitch angle segments with threadtypes 1120 and 1121. Segment 1120 utilizes a left-handed thread andsegment 1121 utilizes a right-handed thread.

FIG. 11 c depicts an example novel connector featuring several segmentswith grooving (thread) type 1140, a segment with thread type 1120 and asegment with thread type 1121. Segment 1120 utilizes a left-handedthread and segment 1121 utilizes a right-handed thread.

FIG. 11 d depicts an example novel connector featuring two segments withgrooving (thread) type 1140, one segment (set) with spline grooving type1130, a segment with thread type 1120 and a segment with thread type1121 (see also FIGS. 1 and 2 ). It is understood that similar systemsutilizing multiple spline sets (segments) 1130 can also be used inconnectors featuring also segments type 1120 and/or 1121, in connectorsutilizing only segments type 1140 and sets type 1130, see FIGS. 1, 2, 11g through 11 j, 111 through 11 p, 11 r or/and 11 x for examples.

FIGS. 11 e and 11 f depict example novel connectors featuring known typeof axisymmetric, zero-pitch angle grooving 1140 that is utilized totransfer axial and bending loads between box 1100 and pin 1110 with keyinserts 1107, 1117 essentially following local taper angles of the pitchdiameter surfaces 1111 of box 1100 and pin 1110. Any geometrical shapesand types of key inserts 1107, 1117 can be used. It is noted however,that the key-grooves and the key-inserts need not necessarily follow thelocal taper angles in many similar connectors. They may or may not bearranged essentially in straight lines and in addition to being arrangedessentially in axial (meridional) planes, they can also be arranged atnon-zero angles to the said axial (meridional) planes of the said novelconnector.

Although that does not necessarily need to be the case, it is preferredthat key inserts have as slim design as possible, in particular in theradial direction of the connector. If feasible, the grooving used toinsert the keys utilized in this invention should preferably notpenetrate inside the material of box 1100 or pin 1110 deeper thangrooving type 1140, or/and types 1120 or/and 1121 if also used in thesame connector (see also FIGS. 3 and 4 ).

However, in particular where the length of the said connector is theissue, or when the axially symmetric grooving is very shallow, deepergrooving than that outlined above may need to be used with key grooving1107, 1117 utilized in the said novel connectors. Shallow grooving 1107,1117 may weaken bending load capacities of connectors only minimally.

Non-zero pitch thread segments 1120, 1121, while used separately wouldonly allow a reliable torque transfer in one rotational direction, thatwhich tightens the tapered thread. Applying a torque in the oppositedirection would have unscrewed the connection. Both these facts are wellknown to those skilled in the art, because they are widely used inthreaded connections, including for example tapered threaded drill-pipeconnectors. However, in novel connectors the unscrewing of either thread1120 or 1121 is prevented because of the interlocking with other typesof grooving 1140, 1121, 1120, or/and 1126, 1125 respectively and novelconnectors like for example those shown on FIGS. 11 a through 11 d, 11k, 11 o through 11 v and/or 11 x are very effective in the transfer oftorsional loads in both opposite rotational directions. In novelconnectors featuring only segments with thread direction 1120 (see FIG.11 a ) or 1121 (see FIG. 11 k or/and 11 q) the unscrewing is preventedby interlocking (via an axial load) on axisymmetric grooving 1140. Onconnectors that utilize non-zero pitch angle thread 1120 and 1121 (FIGS.11 b, 11 c and 11 d ) thread 1120 is torsionally interlocked against theopposite thread, with grooving 1140 and in the case of the system shownin FIG. 11 d spline set (system) 1130 helping additionally. Interlockingin the torsional load direction is also effected simultaneously with anyother structural arrangements used optionally, or in order to increasethe torque transfer capacities of novel connectors, see multipleexamples shown herein.

FIG. 11 g features spline (rows) sets 1130 arranged outside concentric,zero pitch grooving 1140 arranged along interface 1111 of box 1100 andpin 1110.

FIGS. 11 h through 11 j feature each several spline (rows) sets 1130arranged interchangeably between concentric, zero pitch thread 1140arranged along interface 1111 of box 1100 and pin 1110.

FIG. 11 k depicts an example novel connector featuring two segments withgrooving (thread) type 1140 and one segment with grooving (thread) type1121. The example shown in FIG. 11 k equally represents its mirror imagewith a replacement of grooving (thread) type 1121 with grooving (thread)type 1120, as shown on FIG. 11 a.

FIG. 11 l depicts an example novel connector featuring three segmentswith grooving (thread) type 1140, two segments (sets) of splines 1130arranged between the segments of concentric threads 1140 and key system1107.

FIG. 11 m depicts an example novel connector featuring four segmentswith grooving (thread) type 1140, three segments (sets) of splines 1130arranged between the segments of concentric threads 1140 and two systemsof fitted shear pins at each connector end.

FIG. 11 n depicts an example novel connector featuring four segmentswith grooving (thread) type 1140, three segments (sets) of splines 1130arranged between the segments of concentric threads 1140 and systems ofdog-clutch teeth 1160 at each connector end.

FIG. 11 o depicts an example novel connector featuring four segmentswith grooving (thread) type 1140, three segments (sets) of splines 1130,single segments of non-zero pitch threads 1120 and 1121 each, andsystems of fitted shear pins 1150 at each connector end.

FIG. 11 p depicts an example novel connector featuring four segmentswith grooving (thread) type 1140, three segments (sets) of splines 1130,single segments of non-zero pitch threads 1120 and 1121, a system (set)of fitted shear pins 1150 near the outside metal seals and a system(set) of dog-clutch teeth 1160 near the inside metal seals.

FIG. 11 q depicts an example novel connector featuring two segments withgrooving (thread) type 1140, one segment with right-handed thread 1121and systems (sets) of fitted shear pins 1150 at each connector end.Example novel connector shown in FIG. 11 r implements a combination of 5structural torque transfer arrangements featured herein implemented in asingle design.

FIG. 11 r depicts an example novel connector featuring three segmentswith grooving (thread) type 1140, two segments (sets) of splines 1130,single segments of non-zero pitch threads 1120 and 1121 each, a system(set) of keys 1107, a system of fitted shear pins 1150 near the outsidemetal seals and a system of dog-clutch teeth 1160 near the inside metalseals. Example novel connector shown in FIG. 11 r implements acombination of 6 structural torque transfer arrangements featured hereinimplemented in a single design.

FIG. 11 s depicts an example novel connector featuring two segments eachof non-zero pitch threads 1120 and 1121, four segments in total.

FIG. 11 t depicts an example novel connector featuring single segmentseach of non-zero pitch threads 1120 and 1121 and a system (set) ofdog-clutch-teeth 1160 arranged near the inside metal seals.

Note that FIGS. 11 s through 11 v do not feature axisymmetric thread1140, which is acceptable, because each of threads 1120, 1121, 1125 and1126 also transfer axial and bending loads. In fact threads 1120, 1121,1125 and/or 1126 can be used in novel connectors without a use ofzero-pitch segment(s), providing that they are interlocked with at leastone of the other structural torque transfer sets: splines, keys, fittedpins, dog-clutch pins or even other segment(s) of thread 1125, 1126,1120 and/or 1121 respectively (i.e. those in the same directions, i.e.same-handed, see FIGS. 11 u and 11 v ), providing that they usesufficiently differing pitch values, so that torsional interlockingwould occur. It is, however, preferred to use pairs of opposite-handedthread segments with thread interlocking in mind; opposite-handed pairsmeant as pairing left-handed thread segments with right-handed segmentsand vice versa.

FIG. 11 u depicts an example novel connector featuring a segment ofright-handed thread 1121 and a same-handed, i.e. also right-handedsegment of thread 1126 having a pitch differing from that of threadsegment 1121.

FIG. 11 v depicts an example novel connector featuring a segment ofleft-handed thread 1120 and a same-handed, i.e. also left-handed segmentof thread 1125 having a pitch differing from that of thread segment1120.

FIG. 11 w depicts an example novel connector featuring three segmentswith grooving (thread) type 1140, a segment (set) of keys 1107, twosystems (sets) of dog-clutch teeth 1160 at each connector end twosystems (sets) of fitted shear pins 1150 at each connector end.

FIG. 11 x depicts an example novel connector featuring three segmentswith grooving (thread) type 1140, two segments (sets) of splines 1130,single segments of non-zero pitch threads 1120 and 1121 each, a system(set) of keys 1107 and systems (sets) of dog-clutch teeth 1160 near eachend of the connector. Example novel connector shown in FIG. 11 ximplements a combination of 5 structural torque transfer arrangementsfeatured herein implemented in a single design, with a system of fitted(shear) pins not used.

Pitch angles of threads 1120, 1121, 1125 and/or 1126 should be selectedcarefully in the design. Large, close to 90° absolute values of thosepitch angles are more effective in the transfer of torque and lesseffective in the transfer of the axial and bending loads, vice versa forsmall pitch angles approaching 0°.

FIG. 12 depicts schematically a segment of a novel connector combiningthe dog-clutch and the fitted shear pin principles. The high torquetransfer region is located near external metal seals 1285 and the torquebearing protrusions extend partly through the wall thickness of box 1200and they match cavities in pin 1210.

Pins 1290 or 1295 are tight fitted in cavities of box 1200 and pin 1210.Pins 1290 can have uniform cylindrical shape or pins 1295 can be of aslightly tapered shape (not shown) that would not be visible on thedrawing, if shown. Optionally, stepped fitted pin design 1291 can beused in various implementations of this invention, as shown on FIG. 12 .Optionally pin segment 1291 and the box region where it is inserted canbe threaded, as designated with annotation 1292 in order to highlightthat option (see also FIG. 18 b ). In a case the stepped fitted shearpin shape is selected, the stepped pin nest, threaded or not threaded,can be located in pin 1210, or it can be located instead in the box 1200part of the connector, if preferred so, without affecting thefunctionality of this invention.

FIG. 13 depicts schematically a segment of a novel connector between box1300 and pin 1310 that combines optionally the dog-clutch and the fittedshear pin principles. The high torque transfer region is located nearinternal metal seals 1395 and the torque bearing protrusions extendpartly through the wall thickness of box 1300. Fitted shear pins aredepicted in fully inserted and partly inserted positions 1390 and 1391,respectively. Remarks already provided with descriptions of otherdrawings also apply to FIG. 13 .

FIGS. 14 a through 14 e and 15 a through 15 c show novel connectorsdesigned for relatively low design pressures to medium pressures with anobjective to considerably decrease the assembly/disassembly fluidpressures in comparison with those used typically in known Merlin™family connectors. For known connectors the assembly/disassembly fluidpressures increase with the reduction of connector size—lower hydraulicpressures are used for larger diameter connectors. For example for aknown, high pressure production riser Merlin™ family connector havingOD=8.625″ (219.1 mm) the assembly/disassembly fluid pressure required istypically very high. The novel connector designs shown in FIGS. 14 athrough 14 e and 15 a through 15 c have considerably smaller ODs than isthe 8.625″ regarded at present as the minimum feasible for the designsof known Merlin™ family connectors. In spite of the above, thanks to thedesign modifications introduced it was possible to considerably reducethe assembly/disassembly pressures required, to the extent that it mayeven be practicable to use compressed gas as the assembly/disassemblyfluid. At the same time it was possible to achieve the overall length ofthe connectors assembled between the weld necks, as shown on FIGS. 14 aand 15 a of the order of 75% of the tubing (piping) OD. The overlapsbetween the boxes and the pins were around 60% of the ODs of the tubing(piping). Depending on the design loading of novel connectors featuringsimilar geometries it may be feasible to decrease the numbers and thepitch of threads used, etc., which may allow to reduce the length to ODsratios and the overlap to ODs ratios even further.

The structural stiffenings of novel connectors shown on FIGS. 14 athrough 14 e and 15 a through 15 c are represented schematically asinfinitesimally thin shells for clarity of geometries shown.Simultaneously with the achievements highlighted in the paragraph aboveconsiderable material and weigh savings were achieved, which may beadvantageous in some applications.

Novel connectors shown on FIGS. 14 a through 14 e and 15 a through 15 ccan be built conventionally (traditionally) by welding the stiffeners tothe box and the pin, subdividing the fairing plate/screen into smallerpanels and welding those to the webs. The hatchings through themid-thicknesses of those meridionally-planar stiffeners 1431, 1432 shownin cross-sections are hatched as traditionally fabricated components.The preferred manufacturing method of novel connectors and theircomponents shown in FIGS. 14 a through 14 e is 3D printing. In a casepin 1410 had been built using 3D printing, the hatchings of stiffeners1431 and 1432 would have been the same as that of pin 1410.

The novel structural modifications introduced on FIGS. 14 a through 14 eand 15 a through 15 c are the following:

-   -   Novel variations in the stress IDs 1411, 1511, tapering of the        stress ODs 1415, 1515 of boxes 1400, 1500, or their        approximations;    -   Optional tapering of the inside (stress) diameters 1417 of pin        1410, or its approximation;    -   Providing optional planar ribs 1421, 1521 and/or curved ribs        1523, 1524, 1525, optionally forming stiffening patterns like        for example helicoidal pattern 1526, box pattern 1527 or        honeycomb pattern 1528 on boxes 1400, 1500;    -   Providing optional planar ribs 1431, 1432, 1433, 1434, 1435,        1436, 1437, 1438, 1439, 1440, 1441 and/or curved ribs 1455,        1456, 1457, optionally forming stiffening patterns like for        example helicoidal patterns 1460, box pattern 1461, honeycomb        patterns 1462, 1463 or other patterns 1464, 1465, 1466, 1467 on        pin 1410;    -   Introducing optional web stiffeners 1802, see also examples of        other web stiffener arrangements feasible 1801, 1803, 1804,        1805, 1806 and 1807, see FIG. 18 a . Web stiffener 1801 shown is        double-sided, stiffeners 1802 through 1807 are shown as        single-sided for the sake of examples only. A use of similar        double sided web stiffeners or any other shapes meeting        particular design objectives is also feasible.    -   Fairing the IDs of the pins to constant design values with        optional fairing plates or screens 1471, 1472, 1473 and 1474;    -   Introducing stress relieving cut-outs 1481, 1482 and similar        (shown, but not annotated) that also allow fluid flow across        stiffeners;    -   Adjusting distances between the ends of the threaded segments        and inside and outside nipple seals in order to control the        meridional bending stiffnesses of pins and boxes in those        regions.

Optionally, but preferably in most cases cylindrical fairing plates1471, 1472, 1473, 1474 can be provided with pressure equalizing holes,slots screens, etc., so that the fluid pressures are substantially thesame in the flow and in the cavities formed by pin stiffeners andfairings. Design details can vary considerably depending on the fluidtransported and wide ranges of design conditions. In particular pressureequalizing holes 1491 shown on FIGS. 15 a and 15 b may be suitable fortubing or piping connectors transporting gases with not too big flowtransients. High pressure, flow and thermal transients, multiphase flow,a presence of solid sediments, draining requirements, etc. may requiremore and larger holes, slots or screens with wide ranges of solidityratios. Hole or slot structural or thermal reinforcements like forexample 1817 (FIG. 18 b ) may be required in cases of high pressure,flow and/or thermal transients.

For slender connector designs where reducing component weight isimportant the design of inside (and outside) nipple seal regions mayrequire novel local connector wall thickness increase(s) near one orboth ends like that depicted on FIG. 14 a as 1403. External and internalstructural reinforcements can be used in order to provide acceptableload paths, to optimize hoop stress loading, meridional bendingstiffness and to prevent buckling during the assembly and/or inoperation. Stiffening means arranged on the outside surface of said boxcan optionally include implementations featuring fiber reinforcedplastic stiffenings of said box of said mechanical connector.

FIGS. 14 a through 14 d, 15 b and 15 c show for sake of examples singlerows of honeycombs and/or box stiffeners. However, many more rows ofsandwich stiffeners like those could be used instead in their places, asit is often practiced in engineering. The webs corresponding would bemore slender, the resulting straining of boxes and pins would be moreuniform and even greater weight savings might result. The single row‘sandwich’ stiffeners in FIGS. 14 a through 14 d, 15 b and 15 c areshown herein for example, because those are less typical in sandwichpanel engineering. External sandwich panel fairings on box stiffeners(not shown) can be also used. All the above mentioned stiffener designscan also be used on novel high pressure connectors like those shown inFIGS. 16 and 17 .

FIG. 16 depicts an example detail of a novel connector designed forrelatively high design pressures and limited space available along theconnector axis. The design shown features outside tubing or pipingdiameter considerably smaller than OD=8.625″ (219.1 mm). The ratio ofthe length of the connector assembled (between the weld necks, as shown)to the outside diameter of the tubing is just above 60% and the ratio ofthe box/pin overlap to the outside tubing diameter is around 40%. Again,with further design optimizations, a reduced number of threads, asmaller thread pitch, smaller heights of the thread teeth, etc. asgoverned by a particular design premise achieving even smaller lengthand overlap ratios might be achievable. The materials used for novelconnectors featured herein, and in particular for those depicted onFIGS. 14 a through 17 are also of importance. The use of very highstrength materials, in particular where their elastic moduli are notvery high may also help in achieving very high design parameters ofnovel connectors at relatively small piping or tubing diameters (forexample titanium and some nickel based alloys). Because of the highdesign pressure and the objectives to minimize the overall and box/pinoverlap lengths the assembly/disassembly pressure required is relativelyhigh, consistent with those used in the known Merlin™ family connectortechnology.

Box 1600 features multiple tapers 1615 on its outside diameter andmeridional ribs 1621. More complex rib patterns like those shown onFIGS. 15 a through 15 c and highlighted in a discussion correspondingcan be also used, if required. Pin 1610 features inside (stress)diameter tapering 1617 or its approximation, and inside diameter fairingor screen 1671. Fairing 1671 can be optionally provided on the inside ofpin 1610 with pressure equalizing holes or slots (not shown) in order toequalize pressure between the tubing (piping) and pin cavity 1675. Theoptional pressure equalizing holes or slots are required for mostdesigns.

All the connector components shown are represented as solids on FIG. 16. This connector can be constructed using conventional technology or 3Dprinting. A printed connector is shown on FIG. 16 .

FIG. 17 depicts an example of a novel HP connector design featuringaxisymmetric threads and shear fitted pins 1790, 1795 are arranged intwo staggered rows near the outside metal (nipple) seals. Basic designof the novel connector shown on FIG. 17 is similar to that shown on FIG.16 . Fairing 1775 is provided for sake of an example on an outside ofbox 1700. Fairings could be similarly provided on the outside of boxesshown on FIGS. 14 a, 15 a through 15 c and/or on FIG. 16 as well as onan outside of a box of any novel connector introduced herein.

Pins 1790 or 1795 are tight fitted in cavities of box 1700 and pin 1710.Pins 1790 can have uniform cylindrical shape or pins 1795 can have aslightly tapered shape (not shown) that would not be visible on thedrawing, if shown. Stepped fitted pin design is used in variousimplementations of this invention, as shown on FIG. 17 , but a use ofnot-stepped pins is also feasible. Optionally, pin segment 1792 and thebox region where it is inserted can be threaded, see FIG. 18 b . In acase the stepped fitted shear pin shape is selected, the stepped pinnest, threaded or not threaded, can be located in pin 1710, or it can belocated instead in the box 1700, if preferred so, without affecting thefunctionality of this invention. Allen wrench (key) nest 1797 can beprovided, see FIG. 18 b , screwdriver slot, Phillips or torx nest, etc.can be used instead. All the connector components shown are representedas solids on FIG. 16 . This connector can be constructed usingconventional technology or 3D printing. A printed connector is shown onFIG. 17 .

FIGS. 18 a through 18 c depict example design details of novelconnectors.

FIG. 18 a depicts several examples of web stiffeners that can be used atany location on any stiffener on novel connectors described herein.Stiffener examples are shown schematically as shells and they aremounted on a demonstration web 1808. Stiffener 1801 is a double sidedstiffener, stiffener 1801 is a similar single-sided stiffener. Any otherweb stiffeners, shown or not shown can be single-sided or double-sided.Other examples shown are angle stiffener 1803, T-stiffener 1804, bulbplate stiffener 1805 (with the bulb shown as a solid component),undercut stiffener 1806 and double-undercut stiffener 1807.

FIG. 18 b shows equalizing hole reinforcing ring 1817 and example fittedpins 1790 and 1795, which are described in the description of FIG. 17 .Reinforcing ring 1817 can be used to strengthen a fairing plate or ascreen in a case of pressure transients or/and it can be requiredbecause of pressure transients associated with high thermal transients.The materials used can be metallic or non-metallic (tungsten, cementedcarbides, crystals like corundum, beryllium, diamond for non-oxidizingflows, etc.).

FIG. 18 c depicts an example of a typical axisymmetric thread used onboxes 1800 and/or pins 1810. Thread generatrix 1820 is that on theloaded side of the thread on box 1800 and thread generatrix 1830 is thaton the unloaded side of the tooth. The loaded sides are those thatresist disassembly of a connector. Angle Θ2 _(b) is measured between thenormal to the box or connector axis (coinciding) and generatrix 1820.Angle Θ1 _(b) is measured between the normal to the box or connectoraxis (coinciding) and generatrix 1830. Thread generatrix 1840 is that onthe loaded side of the thread on pin 1810 and thread generatrix 1850 isthat on the unloaded side of the tooth. Angle Θ2 _(p) is measuredbetween the normal to the pin or connector (coinciding) axis andgeneratrix 1840. Angle Θ1 _(p) is measured between the normal to the pinor connector axis (again coinciding) and generatrix 1850. Angles Θ2 _(b)and Θ2 _(p) are typically greater than zero (preferably approximatelyhalves of angles Θ1 _(b) and Θ1 _(p)), even though designs with anglesΘ2 _(b) and Θ2 _(p) equal to or close to zero have been used. Angles Θ2_(b) and Θ2 _(p) close to zero are superior structurally, but connectorsfeaturing such angles can be very difficult or impossible todisassemble; assembling them can be difficult too. Known connectorstypically use Θ2 _(b)=Θ2 _(p) and Θ1 _(b)=Θ1 _(p), which can also be thecase in novel connectors. However, in many design cases novel connectorsuse mismatching thread angles that is to say Θ2 b≠Θ2 _(p) and/or Θ1_(b)≠Θ1 _(p), see FIG. 19 . The manufacturing tolerances on threadangles Θ1 _(b), Θ1 _(p), Θ2 b and Θ2 _(p) required should be very small(high accuracy required), and each few hundreds of a degree of threadangle mismatch makes a noticeable difference in thread tooth loadingwhen an accurate Finite Element Analysis (FEA) is carried out.Therefore, conservatively connectors can be regarded as utilizing novelgeneratrix angle mismatches when any of the absolute values of mismatchangle |ΔΘ2|=|Θ2 _(b)−Θ2 _(p)| or that of mismatch angle |ΔΘ1|=|Θ1_(b)−Θ1 _(p)| is not smaller than 0.05°, but smaller or larger valueslike for example 0.075°, 0.1°, 0.125°, 0.15°, 0.175°, etc. . . . or evenmore than 0.35° can be selected for the above purpose.

The types of mechanical connectors of long torsional and bending fatiguelife provided with tapering outside diameters of boxes with optionaltapering inside diameters of pins or/and optional radial ribs areimmaterial, all connectors described or/and disclosed herein can beprovided with variable outside stress diameters of boxes, variablestress inside diameters of pins or/and optional ribs. In addition to theconnectors similar to those depicted those shown on FIGS. 14 a , 16 and17 connectors depicted on FIGS. 1 through 11 x can be also provided withvariable outside diameters of the boxes, tapered outside stressdiameters of boxes (or their approximations), with optional variable ortapered inside stress diameters of pins (or their approximations) or/andoptional ribs. The said novel variations and/or tapering of stressdiameters are not limited to those depicted on FIGS. 14 a through 17. Inparticular the taper angles can vary along the boxes and/or pins inorder to provide hoop stress and meridional bending flexibilitydistributions along of the boxes and/or pins optimal for any particularapplication examples shown on FIGS. 14 a through 17 were selectedbecause they feature meeting design requirements that tend to fall ontechnically demanding sides.

FIG. 19 depicts schematically a detail of a cross section of interactingthreads of box 1900 and pin 1910. Optional tooth crest geometrymodifications that result in interference fit are shown exaggerated.

The typical radial interference fit between box 1900 and pin 1910results in normal contact pressures between tooth surfaces 1920 and 1950of pin 1910 as well as 1930 and 1950 of box 1900, respectively.

In addition to the ‘regular’ radial interference fit of the thread, adesign of additional, superimposed interference fits as illustratedschematically on FIG. 19 is carried out so that all the materialstressing of box 1900 and pin 1910 remains in the elastic range. Foraxisymmetric threads, thread mismatch angles ΔΘ1 and ΔΘ2 are in themeridional planes of the connectors, as shown in exaggeration on FIG. 19. For threads featuring non-zero pitch values, thread mismatch anglesΔΘ1 and ΔΘ2 are defined analogously to the above, but the threadmismatch angles are measured in planes normal to crest lines of thethreads. Using generatrices on unloaded and loaded sides of teeth whiledefining the above angles assures that those angles are always measuredin planes normal to crest lines of the threads. With a novel threadmismatch angle between the generatrix of surface 1920 and the generatrixof surface 1930 ΔΘ1>0, an increase of normal contact pressure near tip1970 of tooth of the thread on pin 1910 results in comparison with thecorresponding normal contact pressure distributions in known designs,i.e. those featuring the radial interference fit only. With a novelthread mismatch angle between the generatrix of surface 1940 and thegeneratrix of surface 1950 ΔΘ2>0, additional increase of normal contactpressure near tip 1970 along other parts of surfaces 1920, 1930, 1940and 1950 result. Whenever thread mismatch angle ΔΘ2 is greater thanapproximately thread mismatch angle ΔΘ1 the interference fit resultsalso in bending and shear of tooth of pin 1910 that is defined bysurfaces 1930, 1950 and tooth tip 1970. With slim designs of pin teeththe said bending may also be effective whenever thread mismatch angleΔΘ1≈0, or is negative. Axial interference fit between surfaces 1940 and1950 against interference fit between the outside contact abutmentsurfaces is therefore affected by the said radial interference fits.Elastic bending of teeth interacting results in more even axial and/orbending load distributions along connectors than those that would havetaken place for angles ΔΘ1=ΔΘ2=0 due to the resultant decrease in thespring stiffness of the threads. This effect is more pronounced for‘slim teeth’ threads (and relatively small pitch), than it would be forthreads utilizing greater pitch. FIG. 19 illustrates teeth interactiongeometries featuring essentially rectilinear generatrices of contactsurfaces 1920, 1930, 1940 and 1950, however in general cases some or allof the said generatrices can be curvilinear for more accurate control ofnormal contact pressure distributions along the contact surfaces.

It is well known that end teeth take most of the loading on threadedconnections. For novel connectors designs featuring relatively smallerdesign pressures, smaller axial loads and/or smaller bending loads thanthose typically specified for connectors used on production risersoffshore, using less thread teeth may be acceptable. Thread anglemismatching results in improved, more uniform thread loading along theconnector. That is because of the smaller spring constant of lowerpitch, slimmer teeth. Denser grouping of greater pitch teeth near theends of the thread helps additionally, because of the greater springstiffnesses of those teeth than are those of the regular pitch teeth. Insuch arrangements more of the load of the regular end teeth istransferred to the nearby increased pitch teeth, see the thread on pin1810, FIG. 18 c , where only 3 ‘slim’ teeth are used between the end‘thick’ tooth and the next ‘thick’ tooth. Similar approach was utilizedin the designs shown on FIG. 14 a, 15 a through 15 c , 16 and 17, in allcases on both thread ends.

Maximum contact pressures in regions of pin tooth tip 1970 increase theeffectiveness of leak prevention along the surfaces interacting of box1900 and pin 1910. In cases where temperature gradients exist along theconnector, heat transfer coefficient (according to the Fourier Law)across the contact surfaces is higher where higher contact pressuresoccur. Other important factors affecting the heat transfer are forexample the roughness and the waviness of the contact surfaces as wellas film heat transfer coefficients (conduction, convection andradiation, whichever applies) of fluids, vacuum (or solids, see FIG. 20) filling voids and gaps between the contact surfaces.

Whenever the tooth crest shape modification principle illustrated onFIG. 19 is reversed (increased contact pressures in the region of boxtips 1960, not shown on drawings) similar crest shape modificationswould have similar positive effect on leak-proofing, but the structuraleffects would be decreased, because there is normally a gap between theinside abutment surfaces. However, the said reversed tooth crest shapemodification principle may enhance heat transfer between pins and boxesin installations where connector pins 1910 tend to be hotter thanconnector box 1900.

FIG. 20 depicts a detail of connector box 2000 interacting with pin 2010featuring a novel use of assembly/disassembly fluid 2025 solidified incavities. After assembly at elevated temperature the connector is cooledin a controlled way, so that the desired excess of assembly/disassemblyfluid is removed, after which plugs 2015 are inserted into the fluidoutlet ports and fluid inlet port(s) is (are) also plugged allowing theremaining fluid to solidify in all the voids during a controlledcooling. Axial and bending load cycling can be optionally used duringthe fluid solidification stage.

For all novel connectors, and in particular for those featuring lighterdesigns, care should be taken to make sure that the design properlyaddresses and prevents occurrence of buckling in all the modes bucklingcould potentially occur. That is in particular important during theassembly/disassembly and in operation. Buckling potential remains oftenunidentified during finite element analyses (FEAs), and otherestablished engineering methods are used instead. For novel connectorsone can mention for example cardioidal buckling of pin, bellows-modebuckling of pins and/or boxes, shell buckling and/or stiffenerweb-buckling of optional fins. Those may be caused by theassembly/disassembly fluid pressure and/or by combinations of loadsunder various loading scenarios.

Suitable safety measures must be applied at all times, while taking intoaccount that considerable potential energy can be stored in theconnector system during operations, during assembly and disassembly, andparticularly so whenever highly compressed gas is used.

High torsional capacity arrangements can involve a single set of meanslimited to one connector region or any of the high torsional loadcapacity means can be mixed in the design of any particular connector.It is not practical to depict on drawings all the implementations ofthis invention involving all novel combinations of configurationsfeasible, accordingly FIGS. 1 through 20 should be treated as examplesonly, selected for the explanation of operational principles of thedesigns under this invention.

Newly designed connector elements should be dimensioned for specificdesign requirements. In particular some novel connectors require highstatic and fatigue torsional and bending capacities of the same order,while for example their design axial load capacities may be a great dealsmaller than are those typical of the applications of the Merlin™ familyconnectors. In such cases novel connectors may require smaller numbersof threads similar to those shown herein as 160, 165, 350, 355, 1140,etc., and the teeth profiles used may be ‘slimmer’. The designs of suchnovel connectors may turn up to be more compact than are typically thoseused in Merlin™ family connectors used on a pipe of the same size.Stress analyses, design testing required, etc. are similar to thosetypically used in designing and qualifying known Merlin™ familyconnectors, with torsional load related considerations added. Wheneverthermal loading is involved, including transients, the testing programsmay need to be extended accordingly. The teeth designed to carrypredominantly torsional loads or predominantly bending may have moresymmetrical profiles than are those that carry axial, bending and axialpre-stressing loads, because typical loadcases of novel connectors mayinvolve reversible torsional loads (i.e. clockwise and anticlockwise)and reversible bending loads (i.e. left and right in plane, and left andright out-of-plane) of say an adjacent elbow, while negative andpositive load amplitudes are often similar.

For many novel implementations it is recommended to use a carefullyselected torsional preload of interacting surfaces, which in particularcan be achieved by means of radial preload which results in a desiredcircumferential fit between the surfaces interacting. The use of asuitable torsional preload is preferable for similar reasons as arethose with regard to the axial and bending loading of traditionalMerlin™ family connectors, which is obvious to anybody skilled in theart. For the same reason, whenever a close to 90° pitch angle groovingis used, or splines are used, providing such connectors with optionalexternal ribs that would stiffen the connector in meridional bendingmight be considered in the design optimization. Increasing meridionalbending stiffness of a connector by means of meridional ribs hardlyaffects its bulk torsional flexibility. For the same reason splines maybe often preferred to high pitch angle threads 1120, 1121.

It is noted that the description and figures included herein do notlimit the design range of the novel connectors to only those solutionsdepicted on drawings and/or discussed explicitly. The discussion andfigures included herein characterize whole classes and families of novelconnectors with only some specific representations shown as outlineexamples characterizing broader classes of novel connectors.

For example novel connectors utilizing fitted pins many other but shownshapes of fitted pins used in mechanical engineering (including thosehaving for example square or hexagonal cross-sections) that are suitablefor torque transfer according to this invention, can be also used totransfer torsional loads while being arranged between other box and pinsurfaces, not shown on FIGS. 5, 6, 17 and 18 b. For example, somedesigns of novel connectors may be suitable for placing fitted pin rowsin the cavities of the metal seals, like those shown as 140, at the endof a box, at the end of a pin or in both those locations, see FIGS. 12and 13 . Fitted pins can also be used between dog-clutch teeth 780, 706,716, 990, 906, 916, etc. All such families of connectors feasible arehereby regarded as novel connectors. Connectors featuring other groovingpatterns than are those shown on FIG. 11 a through 11 x or on otherfigures herein are also regarded as connectors according to thisinvention.

Dog-clutch teeth can also be arranged at the ends of metal seals, likethose shown as 140, again at either one or at both connector ends, seeFIGS. 11 n, 11 p, 11 r, 11 w, 11 x , 12 and 13.

Novel connectors can be welded to the ends of pipes to be connected, orthe pins and the boxes forming a connector can be shaped in the actualpipe material used. Typically high yield strength and small grain highquality materials are used for manufacturing novel connectors.Components of novel connectors can be built from materials compatiblewith sweet or sour service requirements; they can be clad or lined,etc., as the design needs require. Those include boxes and/or pinsand/or other components used in the same connector being made ofdifferent materials. Boxes and/or pins and or/other components used inthe same connector can utilize or not utilize weld overlay(s), liningand/or cladding as required. CRAs, titanium alloys, aluminum alloys,magnesium alloys, nickel based alloys, steels and other alloys can beused depending on the design needs. Conventional or novel weldingtechniques, like for example friction welding and 3D printing can beused. Molding or injection molding can also be used with many metals oralloys (example aluminum alloys).

During the design multiple considerations should be taken into account,in order to provide novel connectors with high fatigue strength. Inparticular the accuracy of finish of the surfaces of the connector isimportant for pre-stressing and for high fatigue load applications. Itis recommended in particular that novel connectors be built to highdegree of accuracy and very smooth surface finish. It is recommended toconsider carrying out shot peening, laser peening or equivalent duringthe manufacturing operations. High accuracy grinding and polishingshould also be used, or at least considered. Benefits of thermaltreatment should also be utilized where applicable, including surfacethermal treatment, nitriding, etc. For small diameter connectorsprecision manufacturing technology should be used.

In cases of crisp separations between the axial-bending and torsionalload capacity areas (for example for dog-clutch, key and spline designs)novel mechanical connectors need to be designed against accidentallocking in a similar way to that, which is used in Merlin™ familyconnectors and/or its third party derivations, see for example U.S. Pat.No. 8,056,940.

Whenever a novel connector has to be assembled at a specific relativeazimuth angle orientation of a pin versus a box, it is optionallyrecommended that external markings are provided to facilitate theassembly with that correct azimuth angle. An optional assembly guidesystem can be provided and it can be designed in varieties of ways. Itcan be removable, or it can be left permanently on the connector in use,etc. Subject to specific design requirements for specific connectors theabove recommendations normally apply to most novel connectors.

Merlin™ family connectors and mechanical connectors of long torsionaland bending fatigue life and other novel connectors have excellentleak-proof capability. Metal (nipple) seals at both the inside andoutside diameters feature interference fits, which are very effective insealing. Additional sealing barriers include the concentric, zero pitchthreads, which are radially, circumferentially and axially prestressed,non-zero pitch threads (wherever used) as well as external abutmentsurfaces such as 1459, 1659 that are interference fitted against thethread surfaces normal to the axis of the connector. An optionaladditional sealing barrier can be added by incorporating O-ring(s)elastomeric or metal, metal C-ring(s), E-ring(s), U-ring(s), etc. in thegap between inside abutment surfaces such as 1457 and/or 1657. Theengineer needs to make sure that sufficient draining/exit is provided toremove the excess of the assembly/disassembly fluid after the assembly.Special means may need to be provided for that, like for examplechannels connecting thread tooth cavities, additional outlet ports, ifrequired etc. These may be especially required in cases where thethreads utilize novel thread angle mismatching described above.

In order to improve even further the leak resistance of all connectorsof the types listed herein, in some applications it may be feasible toutilize for assembly and disassembly fluids that would solidify in thedesign range of working temperatures of the said connectors, thusbecoming solid seals, or practically solid seals in cases such as usingnatural or synthetic resins, mastics, or mastics like substances, etc.Assembly/disassembly at elevated temperatures may be utilized for thatpurpose, but that need not necessarily be the case, like for example ina case of using liquid mercury or of sodium-potassium eutectic (NaK) atenvironmental temperatures for connectors operating in low temperaturesincluding cryogenic temperature ranges. The fluids used can benonorganic, organic and in particular metallic.

Care should be taken on the physical, chemical, electro-chemical, toxicand metallographic properties of the solidifying fluids used.

The physical properties include in particular the temperatures andpressures of the triple points of the fluids and their criticalproperties, the boiling temperatures, as well, the temperatures ofrecrystallization as well as the degrees of shrinkage (or otherwise)while solidifying. The chemical properties involve the fluidreactiveness with the connector materials, with the fluids transportedin the pipelines or tubing as well as with other materials used. Thechemical and electro-chemical properties of importance also includecorrosion related aspects. Fluid toxicity can also be of importance. Forexample mercury cannot be used in aeronautical applications that utilizealuminum alloys. The metallographic properties include the subjectivityto diffuse into structural alloys (or other materials used), etc.,(hydrogen induced brittleness, desirable or undesirable nitriding,etc.). One can also mention here phase changes in solid sealants thatoccur with the change of temperature, because of natural changes incrystal structures, of the solubilities of alloyed phases in otheralloyed phases etc., including eutectoidal changes etc.

Ideally the fluid used would be liquid at the temperature of applicationand would solidify with required shrinking, if any is required at all,and remain solid in the entire range of the design conditions. Thesolidification shrinking, as prescribed may be beneficial, because itmay partly or wholly take care of the need to remove excessassembly/disassembly fluid at the last moments of connector assembly.Such solid seals would fill all the gaps very effectively and work likeO-rings. Also ideally the solid seals would have lower material strengththan that of the connector material, so that they could easily deformplastically under the action of changing loads. The temperature ofrecrystallization would ideally fall below the design operational rangeof temperatures, which would enable unlimited ductility under dynamicloading.

For applications where it could be difficult or impossible to find afluid/solid substance meeting all the above criteria, the work below thetemperatures of recrystallization may be acceptable in someapplications, in particular when the solid seal material is temporarilyheated above its temperature of recrystallization. Phase changes due todifferent phase equilibriums with temperature (like for exampleeutectoidal transitions) can have similar effect in lieu ofrecrystallization. Alloys where transitions like that take place andalso other alloys should be examined thoroughly in order to make surethat no hardening like phenomena that could be unacceptable take placeno undesirable phases be formed, etc. Also in some applications it maybe acceptable to allow temporary melting of the sealing material in thedesign temperature ranges followed by re-solidification. In cases wherethe liquid material can boil, extreme care would be required in order tomake sure that the vapors do not cause cavitation damage or otherstructural damage as well as that the subsequent re-solidificationhappens slowly enough to evenly re-distribute the seal material when itremains liquid, and not to upset the connecting functions of theconnector. It is preferred to avoid boiling in the design temperatureranges. Just in case, fluid inlet and outlet plugs can be provided withpressure overload safety valves.

For applications in the environmental ranges of working temperaturessealing materials also used as primary coolant in nuclear reactors canbe considered. Those include mercury, lead, lead-bismuth eutectic,sodium, potassium, sodium-potassium eutectic (NaK). Other materialsinclude for example aluminum, aluminum alloys, copper, copper alloysincluding bronzes and brasses, lithium, lithium-sodium eutectic, tin,bismuth, zinc, magnesium, low melting (fusible) alloys like Rose'smetal, Wood's metal, Field's metal, Darcet's alloy, safe metal, Low 117,Low 136, bend metal, Mellotte's metal, matrix metal, base metal, trumetal, cast metal, etc. Other known metals and alloys, in particularbinary, ternary, etc. eutectics specially designed for particular designconditions can be also used. For example a feasibility of formations ofbinary lithium-potassium and ternary lithium-sodium-potassium eutecticscan be investigated, and if feasible, their properties can beinvestigated and evaluated for use as liquid/metal seals. Many of theabove listed alloys have melting temperatures considerably below theboiling temperature of water, accordingly boiling water or water steamcan be conveniently and economically used during the novel connectorassemblies/disassemblies. Some remain liquid even below the water icemelting temperature.

The use of metallic or alloyed liquids/solid sealants can be ofparticular benefit where good heat transfer properties are requiredbetween pins and boxes. Many alloys feasible are good solders, and whenapplicable good solder like wetting of connector materials can bedesirable both to improve solid to solid heat transfer and the sealingproperties. Suitable flux substances can be added. Sealant density canbe also of importance, however where the volumes of the sealant aresmall, the sealing and/or conduction benefits may outweigh the increaseof weight of the connector.

INDUSTRIAL APPLICABILITY

Known Merlin™ family connectors are used primarily for connecting tendonand rigid riser, including Steel Catenary Riser (SCR) joints. In thoseapplications tension and bending loads are high, while torsional loadsare very small. Use of Merlin™ family connectors have been at leastsuggested for rigid jumper joints, however such a use would be limitedto those jumper connections that do not see very high torsional loads.

Novel connectors are suitable for use in rigid jumpers subject to veryhigh static and fatigue torsional and bending loads. For examplecomplicated three dimensional rigid jumpers are often used in ultradeepwater.

Simple shaped inverted ‘U’ or ‘M-shaped’ rigid jumpers are often used toconnect subsea wellheads with Pipeline End Terminations (PLETs) orPipeline End Manifolds (PLEMs). Those are fitted at ends of subseapipelines that expand thermally in their longitudinal directions. PLETsand PLEMS slide on their mudmats imposing torsional loads on thevertical segments of the jumpers and connectors and bending loads on theremaining segments of those jumpers. Whenever the jumpers are short,high torsional loads must be resisted by the connectors. Novelconnectors are more suitable for the use with inverted ‘U’ and‘M-shaped’ rigid jumpers than are known Merlin™ family connectors, andthey are more economical to use than collet connectors are.

Another class of examples of suitable use of novel connectors are thoserequired for connecting elbows and pipe segments in rigid jumper designsof SCR hang-offs disclosed in U.S. Pat. No. 8,689,882 by Wajnikonis andLeverette. Those inventors state that spools resisting rotationaldeflections of the SCRs are subject to high torsional loads; bendingloads are also mentioned.

Newer riser hang-offs according to WO/2016/191,637 ideally require novelconnectors. These connectors are typically subjected to even higherstatic and fatigue torsional and bending loads than are thoseexperienced in SCR hang-offs according to Wajnikonis and Leverette. Inthe presently discussed newer designs, the torsional and bending loadstend to be of the same order of high magnitudes.

In both the older and the newer classes of the said SCR and rigid riserhang-offs the effective tensions are very small, the actual or ‘wall’tensions in those connectors being governed by so called ‘end cap’pressure effects. That implies considerably lower actual or ‘wall’tensions than are those typically experienced by known Merlin™ familyconnectors used for example to connect SCR joints. All the technicalterms used here are used in engineering codes and are familiar to thoseskilled in the art.

Novel connectors can be used to connect pipes made of materials thatcannot be welded together (example steel alloys and titanium alloys) orof other materials that are difficult or impossible to weld. Additionalfields of industrial application may be listed. Because of theirreliability and the extremely low susceptibility to leaks, novelconnectors can be used for piping and pipelines in the chemical, onshoreor offshore cryogenic installations and in the nuclear industry. Inaddition to the above features, novel connectors have very slim designsand low weights. Accordingly, they also deserve to be considered foraerospace applications, in particular cryogenic tubing or piping.

Low cost, high production volumes of connector components used in pipingmade of non-metallic materials, like for example plastics may be anotherpossible field of application. Large numbers of very accuratelydimensioned plastic boxes and pins used in novel connectors can be massproduced for example by casting or by injection molding. When plasticmaterials are used, tooling for assembling/disassembling may be lowpressure hydraulic or pneumatic.

What is claimed is:
 1. A mechanical connector provided with threads onsubstantially matching frustoconical surfaces of a box and a pin, saidsubstantially matching frustoconical surfaces of said box and said pinextending essentially between two sets of nipple seals, whereas one saidset of said nipple seals is located near an end of said box and anothersaid set of said nipple seals is located near an end of said pin andwhereas each said set of said nipple seals incorporates axiallyengaging, substantially cylindrical surfaces with an outside surface andan inside surface of a male substantially cylindrical segmentinteracting radially through a mechanism of a hoop stress withsubstantially matching surfaces of a substantially cylindrical cavity;whereas said threads on said substantially matching essentiallyfrustoconical surfaces of said box and said pin include at least one of:an axisymmetric thread, a left-handed thread, a right-handed thread; andwherein said mechanical connector includes a one or more system ofinterlocking threads designed to transfer torque structurally comprisingat least one of: said left-handed thread interlocking with saidright-handed thread, said axisymmetric thread interlocking with saidleft-handed thread, said axisymmetric thread interlocking with saidright-handed thread, said left-handed thread interlocking with aleft-handed thread having a different pitch, said right-handed threadinterlocking with a right-handed thread having a different pitch.
 2. Themechanical connector according to claim 1, whereas said mechanicalconnector includes an assembly/disassembly fluid remaining liquid duringassembly/disassembly operations; wherein after an assembly operationsaid assembly/disassembly fluid is allowed to solidify in an assembledcondition of said mechanical connector and remains essentially solid,thus becoming essentially a solid seal.
 3. The mechanical connectoraccording to claim 2, whereas the assembly/disassembly fluid ismetallic.
 4. The mechanical connector according to claim 2, whereas theassembly/disassembly fluid is non-metallic.
 5. The mechanical connectoraccording to claim 1, whereas at least one of the box or the pinutilizes friction welding.
 6. The mechanical connector according toclaim 1, whereas at least one of the box or the pin is manufacturedinvolving injection molding.
 7. The mechanical connector according toclaim 1, whereas at least one of the box or the pin is manufacturedinvolving 3D printing.
 8. The mechanical connector according to claim 1,whereas at least one of the box or the pin utilizes traditional weldingfabrication.
 9. The mechanical connector according to claim 1, whereasat least one of the box or the pin is made of at least one of: a highstrength steel, or a corrosion resistant alloy, or a titanium alloy, oran aluminum alloy, or a magnesium alloy, or a nickel based alloy, or anon-metallic material including a plastic material, or at least one ofsaid box or said pin utilizes at least one of a lining or a cladding ora weld overlay.
 10. The mechanical connector according to claim 1,wherein said mechanical connector includes one or more rib strengtheningarranged on at least one of: an inside surface of a pin, or on anoutside surface of a box.
 11. The mechanical connector according toclaim 1, whereas said mechanical connector includes at least one of: aplurality of shear pins, a plurality of keys.